Diversity reception radio receivers are well known in the art. Such receivers have been used to substantially improve radio reception in a changing multipath environment. Diversity receivers are particularly desirable in mobile and portable applications, in which a receiver may be moved into an isolated weak signal area caused by self-cancellation of multipath signals.
One conventional approach to a diversity receiver has comprised a dual antenna space-diversity system, the dual antennas coupled to a switch for selectively coupling one of the dual antennas to a single receiver. During operation the receiver is switched to an alternate antenna in response to a signal received from a currently selected antenna deteriorating below a predetermined switching threshold. This approach has a drawback in that the approach does not always select the antenna having the stronger signal. For example, a currently selected antenna having a signal marginally above the predetermined switching threshold would remain selected, even though a signal from a non-selected antenna is much stronger.
Another conventional approach to the diversity receiver has comprised a dual space-diversity antenna system separately coupled to dual receiver elements for amplifying and demodulating a radio signal received by the dual antennas. Such receivers have typically utilized an electronic switch to select the "best" output signal from one of the dual receiver elements based upon a measurable selection criterion, such as signal-to-noise ratio. Unfortunately, some conventional output signal selection techniques have been slow to respond, possibly causing loss of received information. Also, while the dual receiver approach to diversity reception has provided performance superior to the single receiver approach, it has typically been a power-hungry approach. This is because the dual receiver approach obviously has required double the amount of receiver circuitry and thus double the power of the single receiver approach. Power requirements are an especially important design consideration in battery powered portable receivers, such as selective call receivers, thereby limiting the widespread use of the conventional dual-receiver diversity approach for such applications.
Thus, what is needed is a way of building a diversity receiver that provides the superior performance of the dual receiver approach but does not require double the amount of power compared to the single receiver approach. A diversity receiver is needed that can switch to a better signal source quickly enough to avoid missing any received information.